This invention relates to filtration of blood circulating through a patient""s body, and more particularly to an apparatus and method for filtering blood flowing through a patient""s vein or artery, thereby removing clots and preventing strokes.
In Western countries, pulmonary embolisms and strokes are two of the leading causes of death, disability and mental impairment. Generally, pulmonary embolisms and strokes are caused by the formation of clots in a patient""s bloodstream and the subsequent migration of those clots to undesirable locations. When migratory clots lodge in a blood vessel, they can occlude the flow of blood to vital areas such as the heart, lungs and brain causing a stroke, collapsed lung, or heart attack. At other times, clots may lodge in blood vessels in the extremities and may block the flow of blood to the hands or feet causing adverse effects.
Various methods have been developed for the treatment of acute clotting incidents and to prevent such incidents before they happen. For example, anticoagulants such as warfarin or heparin may be administered during a stroke incident to prevent or reduce clot formation. However, when used in the long term, these drugs interfere with a patient""s clotting ability in response to injury and may have other undesirable side effects. Thus, prolonged use of anticoagulants may not be a suitable treatment for many patients.
Another method sometimes used in the short term to prevent strokes and pulmonary embolisms is the insertion of a filter directly into a patient""s blood vessel. For example, U.S. Pat. No. 5,108,419, issued to Reger et al., discloses a filter assembly for placement in the artery of a patient during surgery that includes a collapsible filter assembly positionable in a blood vessel by use of a catheter. Once in place, the assembly is expanded via a rotary mechanism to deploy a series filters having different pore sizes for sequentially removing smaller particles from the patient""s blood. At the end of the surgical procedure, the Reger device can be recollapsed via the same rotary mechanism and a drawstring, effectively trapping any filtered particulates so that they may be removed with the device. However, the Reger device does not include any provision for dealing with the accumulation of clots and debris over longer time scales. Therefore, the Reger device is not ideal for use to reduce the risk of strokes and embolisms by filtering a patient""s blood over longer periods of time.
Vascular filters have been developed for more long term use as well. The Greenfield vena cava filter is representative of this class of devices. The Greenfield vena cava filter is a small metal device designed to protect against a life threatening condition called pulmonary embolism. The Greenfield filter has six metallic legs that are joined together at the top forming a collapsible conical structure. The Greenfield filter can be inserted into a desired location within a patients vein or artery and deployed to expand the conical structure in a manner analogous to that of opening an umbrella. When deployed, the conical structure of the Greenfield filter can be expanded to a size larger than the resting size of the blood vessel, causing it to press against the blood vessel walls to secure it in a desired location.
Other vascular filters have been developed, but these devices all suffer from the drawback that they may become clogged with clots and may, therefore, result in reduced blood flow through the blood vessel being filtered. When these devices become clogged, they typically must be either surgically removed or cleaned via catheterization, procedures which both pose some risk and discomfort to the patient. For example, U.S. Pat. No. 5,626,605 to Irie et al., U.S. Pat. No. 5,984,947 to Smith, and U.S. Pat. No. 6,013,093 to Nott et al., also each disclose devices for insertion into blood vessels to filter clots from a patient""s bloodstream. Each of these patents discloses a wire or strut based device that can be attached directly to a blood vessel wall to filter clots. Neither of these devices provide a mechanism to detect and/or dissolve clots. Thus they are less than ideal for use in the long term filtration of clots and debris from a patient""s bloodstream.
It can be seen that none of the prior art devices or methods are ideally suited for use to prevent damage due to clot migration in the long term. Therefore, it is desirable to provide a vascular filtration device and method which can be used to filter a patient""s blood in the long term and which can also provide for the detection and removal of clots without requiring catheterization or surgical removal.
Broadly described, the present invention comprises a vascular filtration device for filtering a patient""s blood in situ. In a first exemplary embodiment, the vascular filtration device of the present invention includes a channel for being connected to, or inserted within, a patient""s blood vessel such that a quantity of blood will flow therethrough. A filter is disposed within the channel for collecting clots and debris in the blood. A sensor is also provided for sensing clot and debris collection by the filter and for generating a signal indicative of the need for injection of an anticoagulant or manual removal of the offending clot(s) or debris collected by the filter.
In a second exemplary embodiment the vascular filtration device includes a chamber housing a strainer which is preferably disposed at an angle to the direction of blood flow to allow accumulation of clots and other debris preferentially at one end of the chamber. The chamber and strainer are preferably both composed of physiologically inert materials such as Teflon, which are similar to those used in other long term implants.
In additional exemplary embodiments, the vascular filtration device may also include a secondary chamber wherein the clots may be retained and dissolved via injection of a clot dissolving compound. An optical or blood pressure sensor can be provided to control the injection of the clot dissolving compound in response to changes in blood optical properties or pressure across the filter resulting from clot accumulation. The sensor can either directly control the injection of the anti-clotting compound or can, alternatively, communicate with a remote monitor to signal the patient or a physician of the need for manual injection of a clot dissolving compound into the retention chamber. In another contemplated embodiment, the sensor includes a transmitter to allow remote monitoring of the measured parameters by a hospital or medical center. In yet another contemplated embodiment, the device includes a hinged opening whereby a catheter may be passed in a particular direction through the device to ensure that the vascular filtration device does not interfere with any necessary catheterization procedures.
The present invention also includes a method for using the vascular filtration device AA to filter blood and/or other bodily fluids flowing through a blood vessel or like passageway. The filtration method of the present invention includes the general steps of: positioning a filter assembly in fluid communication with, or within, a patient""s blood vessel; directing a flow of blood through the filter assembly such that the filter assembly acts to retain debris from the blood; and monitoring the accumulation of debris within the filter assembly.
Accordingly, it is an object of the present invention to provide a vascular filtration device which is suitable for long-term use to filter clots and debris from a patient""s bloodstream to reduce the risk of strokes and/or pulmonary embolisms.
Another object of the present invention is to provide a vascular filtration device which allows the detection of accumulated blood clots and provides a signal indicative of the need to administer an anti-coagulant or clot dissolving compound.
Still another object of the present invention is to provide a vascular filtration device which will filter clots and debris from patient""s blood vessel without precluding the passage of a catheter through the blood vessel.
Other objects, features, and advantages of the present invention will become apparent upon reading and understanding the present specification when taken in conjunction with the appended drawings.